The invention relates to a circuit for demand-conforming switching on and off of a load. The load is coupled to a data bus and the circuit has a sensor for detecting activity on the data bus. The invention further relates to a subscriber terminal for an information network.
An information network contains a multiplicity of subscriber terminals which, at a specific point in time, neither receive information nor transmit information because only a fraction of the connected subscribers are regularly in communication with one another in the information network, and the information network is ultimately configured in such a way as well. Many subscriber terminals are therefore in an operating mode in which, although they do not participate actively in the data traffic, they must be ready at all times for accepting a connection to another subscriber. The subscriber terminals contain electrical circuits which consume current even in the standby state, that is to say in the aforementioned operating mode. In many information networks, such as the telephone network, for instance, the power required for the subscriber terminals is fed to the subscriber terminal via the network connection. It is natural, therefore, that the power consumption of a subscriber terminal must be limited to a low value. In other information networks, such as the Integrated Services Digital Network (ISDN), for instance, a subscriber terminal is not provided with any power from the information network. The subscriber terminal is therefore supplied with power from a separate voltage source. However, it is desirable in this case, too, to reduce the power consumption of the subscriber terminal to a minimum.
An apparatus which makes it possible to minimize the current consumption of a telecommunications terminal which is supplied with current by the analouge subscriber line of the telecommunications network is described in International Patent Application WO 95/28793 corresponding to U.S. Pat. No. 5,608,792, issued Mar. 4, 1997. The circuit has a device for detecting a ringing tone in order to be able to switch a voltage supply circuit between two operating modes. The voltage supply circuit has an oscillator which can operate at different frequencies and a DC voltage converter circuit. The oscillator is supplied with power by the voltage between the connections of the subscriber line, which power is transferred to the circuit of the apparatus by the DC voltage converter. A power supply of the apparatus which is independent of the subscriber line is therefore not provided.
A bus system for the ISDN for use in private domestic environments is disclosed in U.S. Pat. No. 5,379,441. The system has a detector for detecting the signal INFO2 of the ISDN on a two-wire subscriber line. The signal is evaluated in order to be fed to a specific subscriber terminal connected to the bus system. For this purpose, relays are used to connect the subscriber terminal addressed by the incoming signal to the bus system. U.S. Pat. No. 5,379,441, however, does not contain any information with regard to switching on and off of a subscriber terminal or the structure of an INFO2 detector.
It is accordingly an object of the invention to provide a circuit for the demand-conforming switching on and off of a load which overcomes the above-mentioned disadvantages of the prior art devices of this general type, in which the average power consumption of a load coupled to a data bus is minimized.
With the foregoing and other objects in view there is provided, in accordance with the invention, in a circuit for demand-conforming switching on and off of a load coupled to a data bus, the improvement including: a sensor connected to the data bus for detecting signal activity on the data bus and for outputting a corresponding signal; a switching device for connecting a load to a voltage source being independent of the data bus, and the switching device receives the corresponding signal and connects the load to the voltage source when activity is detected by the sensor.
The circuit for the demand-conforming switching on and off of a load coupled to a data bus has a sensor. The sensor is able to detect signal activity on the data bus and, in the event of activity, to output a signal which indicates the presence of activity. The circuit is defined by a first switching device, which can connect the load to a voltage source and which is independent of the data bus. The connection is initiated by the signal coming from the sensor. The circuit has the advantage that the apparatus, which, conventionally, would continually have to monitor the activities on the data bus in a standby state, is supplied with power only when activity is ascertained on the data bus. This is advantageous particularly when the power consumption of the load lies above specific limit values in its standby state. The total power consumption of the circuit and the load can be minimized using the circuit according to the invention.
In accordance with an added feature of the invention, there is another switching device connected to the sensor for keeping the load connected to the voltage source when the signal activity at the sensor ceases. The second switching device keeps the load connected to the voltage source when the signal activity at the sensor stops. This is particularly advantageous when the sensor is disconnected from the data bus after the apparatus has been connected to the voltage source, and the signal which indicates activity would thus stop.
In accordance with an another feature of the invention, there is a further switching device for disconnecting the sensor from the data bus after the load has been connected to the voltage source. The third switching device disconnects the circuit from the data bus after the load has been connected to the voltage source. The disconnection of the circuit from the data bus has the advantage that the data traffic on the data bus is not influenced by the circuit and its sensor, over and above a minimum period of time.
In accordance with an additional feature of the invention, there is a disconnecting circuit connected to the sensor for disconnecting the load from the voltage source when a reset signal is received by the disconnecting circuit. In this case, it is particularly advantageous if the reset signal is output by the load. It is thus possible for the load to disconnect itself from its power supply.
In accordance with a further additional feature of the invention, the switching device has a relay and the relay is either an electronic relay or a mechanical relay. In addition, the relay can simultaneously actuate all of the switching devices.
In accordance with yet another feature of the invention, the sensor includes a differential amplifier with input connections connected to the data bus and the differential amplifier has a positive feedback resistor and/or a negative feedback resistor. The circuit has, as its sensor, a differential amplifier whose input terminals are coupled to the data bus. The differential amplifier is preferably equipped with feedback, which is provided either as negative feedback or as positive feedback. In the case of positive feedback, the effect is that even when there is only brief activity on the data bus, the output signal of the differential amplifier continues to rise even when the activity disappears, and consequently actuates the switching device. In the case of a negative feedback differential amplifier, activity which is present at least during the settling process of the circuit is necessary on the data bus in order to actuate the switching device. The actuation of the switching device is preferably additionally delayed by connecting a low-pass filter upstream of the switching device, which filter delays the rise of the output signal of the differential amplifier.
In accordance with yet another additional feature of the invention, the sensor is supplied with voltage by the voltage source. It is particularly preferred for the circuit according to the invention to be supplied with voltage likewise from the voltage source which is independent of the data bus.
With the foregoing and other objects in view there is provided, in accordance with the invention, a subscriber terminal for an information network, including: a load having a data bus; and a circuit having a sensor connected to the data bus for detecting signal activity on the data bus and for outputting a corresponding signal, the circuit having a switching device for connecting the load to a voltage source being independent of the data bus, and the switching device receiving the corresponding signal and connecting the load to the voltage source when activity is detected by the sensor.
In accordance with an added feature of the invention, the data bus is an S0 receiving bus of an ISDN subscriber terminal. The circuit can then be used with particular advantage because the S0 receiving bus in the ISDN is suitable for feeding power to the subscriber terminal only with the addition of relatively expensive transformers.
In accordance with a concomitant feature of the invention, the load and the circuit form a subscriber terminal for an integrated services digital network.
It is particularly preferred to use the circuit in a subscriber terminal for an information network. The parts of the subscriber terminal which lie outside the circuit of the invention then form the load in the sense of the above explanations. In this case, it is preferred for the information network to be an Integrated Services Digital Network (ISDN).
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a circuit for the demand-conforming switching on and off of a load, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.